Vitamin B12 Deficiency Your body stores 1,000-2,000 times as much vitamin B12 as you'd eat in a day, so it can take many years to see symptoms of vitamin B12 deficiency
However, some people cannot take vitamin B12 injections safely, including those with Lebers disease or similar eye concerns, kidney disease, liver disease, iron or folic acid deficiency, an active infection, or those taking medications that may interact with vitamin B12
What Does a Vitamin B12 Shot Do
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When administered by IV, some research suggests it may improve mental clarity, memory, concentration and alertness